The invention is based on a fuel injection nozzle for internal combustion engines. At small injection quantities, a prolongation of the injection time is attained as a result of the throttle restriction in the fuel flow, and thus quieter engine running is attained. Furthermore, the fuel is better prepared in the case of the smaller quantities which are injected during idling and partial load, which brings about both a decrease in the specific fuel consumption and a substantial reduction in toxic exhaust gas components. At larger injection quantities, such as in the upper partial-load range and at full load, the throttle restriction is then made ineffective, so that because of the larger flowthrough cross section there are no throttling losses and there is sufficient fuel preparation. Demands such as this are being made by engine manufacturers and the developers of such injection systems as this, and various solutions are known for meeting these demands. However, these known fuel injection nozzles have the disadvantage that renders the throttle restriction ineffective during the opening stroke is dependent more or less exclusively on the quantity of fuel supplied. Even small differences in the force of the closing spring, for instance caused by partial failure after a period of use, cause a shift in the instant at which the throttle restriction is rendered ineffective, this instant being dependent on the fuel quantity. This results in substantial disadvantages in terms of fuel preparation and consumption as well as of quiet engine operation.
Subjecting the valve needle to the force of at least two springs in a certain relationship to one another has already been proposed to attain this end. These springs effect an abrupt increase in closing force after the pre-stroke because after the pre-stroke the force of the second spring is added to that of the first. However, this proposed solution, which does avoid the disadvantages discussed above, requires the complete restructuring of the injection nozzle in comparison with a nozzle functioning with only one spring; accordingly, in the course of production these elements, which require particular precision of manufacture, must undergo separate production processes.